1. Field of the Invention
The present invention relates to a key switch improved in the feel of actuation and return speed during switch operation by a finger.
2. Description of Related Art
In a key switch arranged on a keyboard as shown for instance in FIG. 3, a key top 101 has a stem 102 extending downwardly from the key top; the stem 102 is slidably inserted in a seat 104 formed on a housing 103 of the keyboard; the lower end of the stem 102 is connected to the top of a rubber spring 105 which is of an inverted cup shape; a pressing portion 106 is formed downwardly from the center of the top of the rubber spring 105, so that when the key top 101 is pushed with a finger, the pressing portion 106 presses a membrane switch 107 disposed below, thereby closing the switch. When the finger is removed from the key top 101 to release the pressure from the key switch 101, the key top 101 is instantly moved back to the original non-pushed position by the reactive force of the rubber spring 105, thus simultaneously opening the switch.
The key top 101, however, is not necessarily pushed from right above on the axis of the stem 102. In some case, it happens that the key top 101 is pushed on the edge with a force applied obliquely to the stem 102. In this case, a force to push the key acts in the horizontal direction on the upper and lower ends of the seat 104 of the housing. Therefore not only does the stem 102 vibrate during vertical movement, giving a feel of hitch to the finger pushing the key top, but the pressing portion 106 of a rubber spring fails to reach the membrane switch 107, with the result that the switch will not be closed even though the key top 101 is depressed. Furthermore, when the finger is removed from the key top 101, the reactive force of the rubber spring 105 will not necessarily be applied uniformly to the lower end of the stem 102. The stem 102, therefore, will fail to smoothly rise and return, and in some cases, will fail to move fully back because of friction between the stem 102 and the seat 104.
The stem 102 and the seat 104 are in most cases made of a material similar to, for instance, ABS resin. In this case, the stem 102 and the seat 104 are likely to stick to each other because of their affinity, resulting in unsmooth sliding.
To solve the above-described problems, therefore, the present invention has an object to provide a key switch which has been improved in the feel of actuation and return speed of the switch when the key top is pressed with a finger.
That is, the present invention provides a key switch, in which when a reciprocally movable key top is pushed, a stem extending from the key top moves in one direction along the axis of reciprocating motion to actuate a switching member; and when the pressure is removed from the key top, the key top will return to the original position. The stem is slidably inserted in the seat formed on the housing of the key switch, and at least one longitudinal groove is formed extending in the aforesaid direction of the axis in the circumferential surface of the stem which is in contact with the inner surface of the seat.
Since there is formed at least one longitudinal groove axially extending in the circumferential surface of the stem which is in contact with the inner surface of the seat, any stress will be dispersed by the longitudinal groove if applied obliquely when the stem axially strokes in the seat, thereby preventing stem vibration.
Key switches are preferably mounted on the keyboard. The key switches have various shapes and dimensions, are all arranged on the entire upper surface of the keyboard, and are pressed by fingers. In this case, because quick and constant finger touch (feel of key operation) is required not withstanding varied switch pushing modes, it is especially preferable to adopt the key switch of the present invention.
In the stem, four longitudinal grooves are formed symmetrically in relation to the axis. It is desirable that the four longitudinal grooves be arranged so that the circumferential sliding surfaces of the stem formed among the longitudinal grooves will be positioned in lateral and longitudinal directions of the keyboard.
Generally, in a keyboard, if a pressure is applied obliquely to the stem when the key top is pushed by a finger, the pressure applied obliquely will act in most cases in the longitudinal and/or lateral direction of the keyboard. Therefore, the stem, if provided with the sliding surface formed longitudinally and laterally, will become less liable to wear and deformation, resulting in improved durability of the keyboard.
It is preferable that the sliding surface of the stem be coated with a lubricant inclusive of fine particles of fluoroplastics or silicone resin. The stem and the seat are in most cases formed of a homogeneous material; in this case, therefore, the key top fails to make smooth up-and-down strokes due to their mutual adsorptive activity. The lubricant including the fluoroplastics particles thus applied to the sliding portions of the stem and the seat serves to lessen friction and to remove the adsorptive power of the parts.